The present invention generally relates to a system and method for providing gamma event detection and X-ray detection systems in an integrated environment and, more particularly, to detecting whether X-rays are inadvertently incident upon the gamma ray detection system.
There are two distinctive types of imaging systems in contemporary nuclear medicine. One type may employ gamma scintillation cameras (GSCs), so-called “position sensitive” continuous-area detectors. The other type of imaging system involves computed tomography (“CT”).
The GSCs are primarily used to measure gamma events produced by very low-level radioactive materials (called radionuclides or radiopharmaceuticals) that have been ingested by, or injected into, a patient. The signals from the GSCs are used to generate images of the anatomy of organs, bones or tissues of the body and/or to determine whether an organ is functioning properly. The radio pharmaceuticals are specially formulated to collect temporarily in a certain part of the body to be studied, such as the patient's heart or brain. Once the radio pharmaceuticals reach the intended organ, they emit gamma rays that are then detected and measured by the GSCs.
Computed tomography systems generate an infinite set of X-ray beam projections through an object to be examined. The resultant detected X-ray data are computer processed to reconstruct a tomographic image-slice of the object. CT systems subject the object under examination to one or more pencil-like X-ray beams from many directions. The X-ray beams passing through the object are attenuated by various amounts, depending upon the nature of the object traversed (e.g., bone, tissue, metal, etc.). One or more X-ray detectors, disposed on the far side of the object, receive these beams and provide analog output signals proportional to the strength of the incoming X-rays. Each detector output is then digitized and computer processed to help produce an image of a slice of the object.
While it may be desirable to integrate a GSC system and a CT system into one piece of equipment (or at least to position such systems in relatively close proximity), a significant problem arises when this is done. In particular, if any X-rays of significant magnitude from the CT system infiltrate the GSC, at best the output of the GSC will be skewed. Indeed, a GSC includes a large area scintillation crystal, which functions as a gamma ray detector and is typically sodium iodide doped with a trace of thallium (NaI(Tl)). The crystal converts high-energy photons (e.g., gamma rays and X-rays) into lower energy photons, i.e., visible light. The relatively high, and constant, energy profile of X-ray events (as compared with gamma ray events) will likely drive the crystal significantly more than would gamma rays, thereby skewing the detection function of the GSC. More likely, the relatively sensitive photochemistry of the scintillation crystal will be over driven by the X-rays and may take a very long time (sometimes hours) to settle and again become useful in measuring gamma rays. At worst, the crystal may be permanently damaged from excessive levels of X-ray radiation.
Accordingly, there is a need in the art for new methods and apparatus for providing an integrated CGS and CT system which can detect whether X-ray events have begun infiltrating the CGS detection circuitry and take corrective action.